Skeletal System

Bone Classification by Shape

Anatomy of a

Typical Long Bone What tissue makes up

articular cartilage?

Describe the functions of the periosteum.

Bone TissueWhat is osteoid?

Differentiate between the organic and inorganic components of the bony matrix (structure and function).

Histology of Bone Tissue

Which cells lay down fresh bone matrix?

Which cells “recycle” bone matrix?

Where are these cells located in bone tissue?

Compact and Spongy Bone Tissue Organization

Bones of the skeleton contain a combination of both types of bone tissue organization.

Which region of the skeleton is the bone at left from?

What type of bone marrow is found within the spaces of spongy bone?

OSTEOGENESIS

Common to both types of bone formation:a) A connective tissue pattern (model) is formed, which is subsequently ossified by osteoblasts.b) Osteoblasts develop from mesenchyme and produce a matrix, becoming osteocytes trapped in lacunae of the matrix:

1) organic = "osteoid"2) inorganic = "calcium hydroxyapatitie"

c) A thin layer of compact bone surrounds areas of spongy bone.

These notes are found on pages 164 & 165 in your course packet.

Osteogenesis - 10 week fetus

Osteogenesis - 16 week fetus

INTRAMEMBRANOUS BONE FORMATION

1. mesenchymal cells fibroblasts collagen fibers membrane(osteoprogenitor cells) (pattern)

osteoblasts begin ossification spongy bone

2. Connective tissue on the surface of the developing bone forms the periosteum(= simple squamous epithelium with bundles of collagen fibers)

3. Ossification of membranes begins at the center:- Osteoblasts on inside of periosteal membranes form 2 thin layers of compact bone over the spongy bone.

Endochondral Bone

Formation

How is it possible that blood vessels can invade the cartilage pattern if cartilage is avascular?

ENDOCHONDRAL BONE FORMATION

fibroblasts collagen fibers1. mesenchymal cells connective tissue chondroblasts hyaline pattern cartilage

osteoblasts w/ blood vessels to begin ossification

Endochondral Bone

Formation(continued)

Differentiate between the primary ossification center and secondary ossification centers.

2. Osteoblasts develop beneath the perichondrium of pattern; mineralization of thepattern causes subsequent degeneration of the cartilage tissue, opening "holes".

3. Blood vessels invade the degenerating cartilage tissue to nourish osteoblasts as theybegin to ossify what remains of the pattern, producing spongy bone.

4. The primary ossification center develops at the center of the diaphysis and formsthe periosteal collar.

-Epiphyses at this stage remain mostly cartilage.-Osteoblasts beneath the periosteum form a thin layer of compact bone over the

spongy bone.

5. Later, secondary ossification centers develop at each epiphysis.NOTE: ossification at both centers occurs in all directions, but is limited by the dimensions of the connective tissue pattern.

6. The medullary cavity is formed by the action of osteoclasts, developed within theendosteum, leaving a surrounding layer of compact bone.

7. As the two centers of ossification (primary and secondary) continue to develop towardeachother and the cartilage pattern is replaced by bone, a plate of hyaline cartilage is leftand remains for a time between the two growth centers at each epiphysis (= epiphysealdisk).

Endochondral Bone

Formation(continued)

From which embryonic germ layer are the tissues of bone derived?

Which bone tissue organization do you think is stronger (and why): spongy bone or compact bone?

PROCESS OF OSSIFICATION

Osteoblast

alkaline phosphotase* Hydroxyapatite (inorganic component)

Golgi apparatus Rough endoplasmic reticulum

mucopolysaccharides + collagen fibers Osteoid(= glycosaminoglycans) (organic component)

* an enzyme which removes HPO4-2 (phosphate) from compounds: Ca+2 + HPO4-2Other ions (eg. Mg++, K+, Cl- CO3-2) are absorbed onto the surface of apatite

Which joint is shown in the x-ray at right?

Indicate the direction(s) of ossification in the x-ray.

What factors influence the longitudinal growth of bone? (see page 165 of your packet)

Bone Growth in Length

Bone Growth in Width

Other factors necessary for normal ossification

Calcium: 1000mg adult RDA; 1200mg for adults over 50; 1300mg for pregnant andnursing women up to age 18, 1000mg for pregnant and nursing women19-50 years

Vitamin C: to produce collagen in the manufacture of osteoid

Vitamin D: for the absorption of calcium in the small intestine (phosphate follows by electrostatic attraction)

Vitamin A: for bone reabsorption and normal ossification

Collagen fibers: stimulate the mineralization of bony matrix

Pyrophosphotase: may prevent mineralization of collagen fibers found elsewhere in thebody

Osteoblastic hormones: thyrocalcitonin, somatotropin (GH), testosterone, and estrogen

Osteoclastic hormones: parathormone, thyroxine, corticosteroids

Load-bearing exercise: mechanism . . . ?

1 cup of milk (1%, 2% or whole) has 300 mg Calcium1 cup lowfat plain yogurt has 415 mg Calcium

Calcium Homeostasis

Average Intake of Calcium in the Typical American Diet

* The "Other foods" category includes eggs (1.7%), fats and oils (0.1%), sugars and sweeteners (0.8%), and miscellaneous foods (2.6%).

Source: Gerrior SA, Zizza C., 1994. Nutrient Content of the U.S. Food Supply, 1909 - 1990. Home Economics Research Report No. 52. U.S. Department of Agriculture, Washington, D.C.

Some Types of Fractures

There are several types of fractures represented in the collection of x-rays posted in the lab.

Read and answer the questions on each x-ray.

For a typical long bone, where do most fractures occur, and why?

Bone Fracture Repair

Describe the roles of platelets and fibroblasts in the early stages of fracture repair.

Where do the osteoblasts come from to form the bony callus?

Bone Fracture Repair (cont’d)

Describe how the repair of bone fractures is similar to embryonic bone formation?